The present invention relates to devices for applying a coating to a surface submerged in a liquid, making it possible to continuously paint in water large submerged areas, such as the hulls of ships. It more specifically relates to a device making it possible to absorb both small defects in the surface to be painted (small protuberances or pits) and larger defects (protuberances and pits, whose size can be several centimeters per meter).
A certain number of devices for painting a submerged surface have already been proposed. French Pat. No. 2,333,583, filed on Dec. 1st 1975 by the Applicants, describes such a device. In general terms, this device comprises means for spreading the coating onto the surface and which move along the latter, as well as means making it possible to exert a given pressure on the spreading means in order to expel the water from the surface to be coated as the displacement advances. According to a first variant, the spreading means are constituted by a cylindrical roller applied to the surface to be coated, whilst the paint supply is provided by a pipe issuing immediately in front of the roller. In a second variant, the spreading means are constituted by a group of rotary disks, the surface of each of these disks which is in contact with the surface to be coated being covered with bristles. The paint is supplied by pipes issuing into a central opening made in each of the disks. In a third variant, the spreading means are constituted by a spatula having two lips, the front lip being hollow. A pressurized gas jet issues into the cavity defined by the front hollow lip in order to remove the water from the surface to be coated, whilst the paint enters the rear cavity located between the two lips. These different devices are applied to the submerged surface, either by means of jacks, or by means of springs.
French Pat. No. 2,184,352 describes a system which also uses one or more rotary brushes having in their central part hard bristles which are used for further removing the water from the surface to be painted, and on the periphery more flexible bristles for smoothing the paint.
These various arrangements have a certain number of disadvantages, particularly with regards to the rotary brushes. Thus, the rotation speed must be sufficiently high to remove the water from the surface to be painted, but if the speed is too high there is also a risk of removing the paint and it is very difficult to find a satisfactory compromise.
Certificate of Addition BF No. 2,369,010 to French Pat. No. 2,333,583, filed on October 26th 1976 in the name of the Applicants, describes an improvement to these devices aiming at improving the coating application conditions, whilst permitting a better adaptation to surface irregularities and a better adhesion of the coating. In a first variant, the paint spreading means are constituted by a roller comprising an outer envelope surrounding a flexible material having an alveolar or honeycomb structure. The outer surface of the envelope is provided with bristles, whilst the alveolar structure of the inner material enables the water to penetrate the latter, in order that the internal pressure is equal to the external pressure, no matter what the immersion depth. The paint is still supplied by a pipe issuing immediately in front of the roller. In a second variant, the roller is replaced by a pad and only its surface in contact with the surface to be painted is covered with bristles. The pad also has an outer envelope surrounding a flexible material having an alveolar structure. In both cases, the flexibility of the tight envelope and of the internal material enables the device to easily absorb surface defects during its displacement.
However, although these devices make it possible to absorb small surface defects in the form of protuberances, such as weld beads, the alveolar flexible material cannot deform adequately to absorb small pits or cavities and these devices are also unable to absorb larger defects called "defects of form" in the remainder of the present text and which are constituted e.g. by sheet metal defects in the form of protuberances or pits over several centimeters per meter. In addition, use has demonstrated that it was not possible to prevent the penetration of paint and its solvents into the interior of the open honeycomb cavities of the inner material of the pads. In operation, and particularly during cleaning, the solvents and the paint enter the pad, which leads to a rapid deterioration of the materials.
Finally, French Pat. No. 2,355,574 describes a device having rotary brushes actuated by motors, themselves connected to a support by leaf springs. Apart from the faults inherent in rotary brushes mentioned hereinbefore, the leaf springs only permit small amplitude movements and this device does not make it possible to absorb large defects of form.